1. Field of the Invention
The present invention is related to a polarized light-emitting device, and in particular, to a polarized light-emitting device for use in LCD backlight unit.
2. Description of the Prior Art
The backlight unit is one of the critical components for the liquid crystal display, LCD, and because the LCD panel itself does not possess the capability for emitting light itself, therefore, it requires having a backlight unit for providing adequate brightness and a light source with even distribution. Currently, LCDs are widely used in monitor systems, notebook computers, digital cameras, projectors, and other electronic products having growth potentials, thereby driving the continued growth of the demand for the backlight unit and its corresponding components.
Referring to FIG. 1, an illustrative structural diagram of a conventional LCD module is shown. The conventional LCD module includes a LCD panel 2, a lower polarizing film 4, an upper polarizing film 6, and a backlight unit 8, in which the LCD panel 2 includes a TFT substrate, an alignment layer, a liquid crystal layer, a color filter, and other devices, for forming as the main component devices for the LCD. The operating principle of the LCD is by means of using the photoelectric characteristics of the liquid crystal material, through applying an outside electrical field to change the orientation direction of the liquid crystal for displaying under different brightness modes, and also using a lower polarizing film and a color filter for displaying the images. The backlight unit of the current LCD is mostly using the CCFL or the light-emitting diode (LED) as the primary backlight light source, in which the LED possesses reduced drive voltage, longer lifetime, higher luminous efficiency, mercury-free, improved color reproduction, and other special features; therefore, the LED seems to possess the potential for replacing CCFL. However, the light as produced by the LED, prior to being transmitted to the LCD panel, due to different refractive indices of the transmitted media, is constrained by the critical angles. In other words, when the incident angle of the incident light is larger than the critical angle, the incident light is totally reflected by the optical film, and is not able to refract through the optical film and to provide the LCD panel with an adequate light source. At the same time, the light of the backlight unit has to penetrate through the lower and upper polarizing films for producing the polarization effect. During the process, more than half of the incident light is absorbed by the polarizing film. Due to the excessive loss of incident light from the LED as described above, it is an important subject in backlight design to improve the transmitted efficiency of the light from the source.